In recent years, polyimides excellent in heat resistance have been used as surface protective films of semiconductor devices, interlayer insulating films, bonding sheets, protective insulating films for printed wiring boards and substrates for printed wiring boards. Further, with thinning and miniaturization of electronic• electric equipment, in the printed wiring board, it is required to package electronic parts and the like high densely. Therefore, required is processing for enabling continuity to be high densely made between conductive layers of the printed wiring board.
Generally, in a manufacturing process of the printed wiring board, via holes and through holes are formed by NC drilling, plasma etching, laser drilling, punching or the like, and plating is applied to the formed via holes and through holes to be continuity between conductive layers. However, in laser drilling used in the case of performing fine processing, it is necessary to form via holes and through holes on a hole-by-hole basis. Therefore, the need makes continuous production by the roll-to-roll method difficult, and is a significant obstacle also in terms of reduction in costs and improvement in productivity.
On the other hand, it is proposed to dissolve and remove polyimide used as an interlayer insulating film by chemical etching to form via holes and through holes. Chemical etching is suitable for processing by the roll-to-roll method. However, a strong reducing agent such as hydrazine needs to be used in chemical etching of polyimide, and inhibits popularization.
Further, generally, polyimide is low in solubility in aqueous sodium hydroxide generally used in the manufacturing process of the printed wiring board. Therefore, the etching rate of chemical etching is not sufficient, and is a significant obstacle in terms of reduction in costs and improvement in productivity. In order to improve solubility in alkali solution, proposed are adhesive compositions using polyimide having alkali soluble functional groups and oxazoline compound (for example, see Patent Document 1).